Cyclooxygenase-2 Overexpression in Colorectal Cancer is Associated with Non-polypoid Growth

Background: Cyclooxygenase-2 is considered to play an important role in colorectal tumorigenesis. The purpose of this study was to clarify the relationship between cyclooxygenase-2 expression and morphology in colorectal cancer. Methods: We investigated cyclooxygenase-2 mRNA expression and type of growth (polypoid or non-polypoid according to Shimoda’s classification) in 69 colorectal cancers by reverse transcription-polymerase chain reaction and histologic examination. Cyclooxygenase-2 mRNA expression was assessed as a ratio relative to cyclooxygenase-1 mRNA expression (cyclooxygenase-2 index). Results: Cyclooxygenase-2 indices in normal colorectal mucosa, polypoid cancer and nonpolypoid cancer were 0.7 0.1, 1.0 0.1 and 1.9 0.1, respectively. The cyclooxygenase-2 index in non-polypoid cancer was significantly higher than in polypoid cancer (P = 0.0002) or normal mucosa (P < 0.0001). No difference in cyclooxygenase-2 index was found between polypoid cancer and normal mucosa (P = 0.67). Conclusions: These results suggest that cyclooxygenase-2 overexpression in colorectal cancer is associated with non-polypoid growth.